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Air Quality and Animal Agriculture: The Basics

Chesapeake Bay water- and airsheds

Agriculture
and Air Quality

Air
emissions from energy production, manufac- turing, and transportation
have been regulated for decades under federal and state law. Increas-
ingly, air emission regulations are being extended to animal
agriculture. But air emissions from agriculture do not come from
smoke stacks or tailpipes and are more diffuse, less visible, and
hard to measure. The difficulty of measurement makes implementation
of regulations and the choice of abatement technologies particularly
challenging. Yet, the impact of emissions from agriculture can have
implications for human health and the environment.

Airsheds

Air
quality problems occur on a range of spatial scales. Some air quality
issues are localized, such as the odor from a swine farm. At the
regional or global scale, the emission of methane and carbon dioxide,
both known greenhouse gases, contrib- utes to climate change. Air
quality regulations are designed to meet air quality standards for
specific geographic areas referred to as airsheds (Figure 1).
Airsheds are atmospheric units that behave in a coherent fashion with
respect to the dispersion of emissions. The size of an airshed
depends on the pollutant. For example, fugitive dust, a common
emission from a feedlot, will be dispersed by winds within a limited
local airshed. This is in contrast with the airshed that applies to
methane and carbon dioxide emissions, which would be considered
global.

Agriculture
and Air Quality

Animal
agriculture is a source of several signifi- cant air pollutants,
including particulate matter, ozone precursors, greenhouse gases, and
odors. Particulates are a mixture of extremely small airborne
particles and liquid droplets (aerosols), which are linked to
respiratory disease in humans. Particulate matter is measured and
reported as a
coarse, often visible particle, PM10
(between
10 and 2.5 microns in diameter), and fine particle, PM2.5
(2.5
microns or less in diameter). Particles discharged
directly from a source, like dust during feed handling or from
poultry barns, are called “primary particles.” In contrast,
ammonia emis- sions from animal agriculture are considered
“precursors” to PM2.5.
Through chemical reac- tions, ammonia can interact with other air
emis- sions, such as nitrogen oxide from combustion emissions,
creating fine particles that contribute to PM2.5
aerosols.
Particles formed by chemical reactions are called “secondary
particles.” Animal agriculture’s direct contribution to PM2.5
is
rela- tively small, but it does account for three-quarters of ammonia
emissions in the United States as a secondary particulate.1
It
is noteworthy that the U.S. Environmental Protection Agency (EPA) considers
PM2.5
to
be a principal cause of haze pollution in the United States.
Ground-level ozone is created in the atmosphere by chemical reactions involving
nitrogen oxides (NOx)
and volatile organic compounds (VOC) in the presence of sunlight.
Ozone in the upper atmosphere is “good ozone,” protecting the
Earth from the sun’s harmful ultraviolet rays. “Bad ozone” is
found at the ground level. Ground-level ozone can cause respiratory
problems for humans and animals and affects the productivity of crops
and plant health. Animal agriculture is a source of VOC emissions
that contribute to ground- level ozone formation.

Greenhouse
gases refer to a range of compounds that affect the amount of solar
energy that is retained in the Earth’s atmosphere. Primary green-
house gases from animal agriculture include methane, nitrous oxide,
and carbon dioxide. Accumulation of greenhouse gases in the Earth’s
at- mosphere is important due to global warming concerns. Animal
agriculture contributes about a quarter of the human-made methane in
the atmo- sphere, primarily from cattle digestive processes and
manure management.

The
most notable air emission from animal
agriculture operations at the local level is odor from manure genera-
tion, storage, and, ultimately, land ap- plication to farm fields.
For some, these odors affect the quality of life and are considered a
nuisance.

Regulation

Under
the EPA’s Clean Air Act (CAA), ozone, nitrogen oxides, and
particulate matter are all regulated as criteria pol- lutants. Odor
is not currently regulated through the CAA. Instead, EPA has tar-
geted two known odor-causing gases to be regulated individually:
ammonia and hydrogen sulfide. Both gases are regulat- ed by the EPA
for other industries due to their toxic nature under the Compre-
hensive Environmental Response Com- pensation and Liability Act
(CERCLA), also known as Superfund, and the Emergency Planning and
Community Right-to-Know Act (EPCRA). As of January 2009, agriculture
is required to report under EPCRA to local emergen- cy management
authorities if ammonia or hydrogen sulfide emissions attain the
reportable threshold level of 100 pounds per day or more. In
Pennsylvania most commercial-scale egg-laying farms would be required
to report ammonia emissions under the existing definition. Recently,
the EPA has suggested that all but the largest animal agriculture
operations should be exempted from these require- ments. However,
even with exemptions, it is expected that emission reductions will be
sought from animal agriculture.

A
study conducted by the National Academy of Science looked at air
emissions from concentrated animal feeding operations (CAFOs) and
“con- cluded that there is no industry wide, scientifically
credible way to estimate emissions.” This report was the catalyst
for the National Air Emissions Moni- toring Study being conducted
during 2008 through 2010 at twenty-two swine, poultry, and dairy
farms nationwide with the intent to collect high-quality data on CAFO
emissions. The results of this study are expected to guide future
regulation of the industry.